1. Field of the Invention
The invention relates to a method and an apparatus for acquiring a target frequency, and more specifically, to a method and an apparatus for acquiring a target frequency of a multi-path signal.
2. Description of the Prior Art
The orthogonal frequency division multiplexing (OFDM) is a multi-path modulating/demodulating technology with high efficiency. The theorem is to use several sub-carrier waves to transmit the data concurrently to improve the data transmitting rate. As implied by the name, OFDM is used for dividing the available bandwidth into several narrow frequency bands to transmit data in parallel through these frequency bands. Due to the fact that the OFDM wireless communication system has advantages of: high data transmitting rate, high bandwidth using rate, and preventing the radio waves from the multi-path attenuation, the OFDM wireless communication system is widely applied to the new generation wireless communication system.
However, the OFDM technology has its drawbacks, such as a high peak-to-average power ratio and a high sensitivity to the frequency error of the sub-channel. Therefore, in the OFDM wireless communication system, how the frequency recovering can be performed to achieve the effect of frequency synchronization is a very important topic.
The conventional frequency synchronizing method for the multi-path signal is done by adding a cyclic prefix in front of the data sector in the signal. After the signal is received at the receiving end, the frequency/phase is estimated by using the cyclic prefix to obtain the synchronizing frequency. However, when the cyclic prefix is interfered, a serious error occurs in the frequency obtained by the phase estimation and causes a serious frequency departure.
Therefore, the main goal of the invention is to provide a method and an apparatus for acquiring a target frequency of a multi-path signal to solve the problems above.